The US State Department called it an "unconscionable terrorist attack".

Hallel was the first young Israeli child to be killed since a wave of violence began in the region in October.

Over the past eight months, Palestinians have killed 33 Israelis and two visiting Americans in wave of attacks, mainly involving knives but occasionally guns or cars.

Israeli forces have killed at least 198 Palestinians, the majority of whom were shot while trying to carry out attacks, according to the Israeli government.

Several young Palestinian children have been killed by Israeli forces, including a brother and sister killed in an Israeli airstrike in Gaza in March.

The 19-year-old stabber is not believed to be part of any organised Palestinian faction and, like many of other young attackers, appears to have acted on his own.

He wrote repeatedly on Facebook about his desire to be "a martyr" and shortly before the attack composed a poem eulogising a Palestinian woman who allegedly carried out a car ramming attack at Kiryat Arba.

The killing poses a challenge for Israel's new defence minister, Avigdor Lieberman.

Mr Lieberman is the head of an ultra-nationalist party and promised tough measures against Palestinians militants but the young "lone wolf" attackers leave him with few targets to focus on.

Israeli forces surrounded the attacker's village of Bani Na'im and are likely to demolish his family's home as part of a policy the Israeli government says deters future attacks.

"Destroying the home of the attacker’s relatives and canceling their work permits is an unlawful collective punishment, causing suffering for family members who committed no crime,” said Human Rights Watch.

The killing comes three weeks after two Palestinian gunmen killed four Israelis as they ate dinner at a restaurant in Tel Aviv.

Two weeks after that Israeli troops killed a 15-year-old Palestinian boy coming home the swimming pool as they hunted for another group of youths who had been throwing rocks at a motorway.